The present invention generally relates to a method of contacting a relatively thick substrate (i.e., having a thickness of greater than or equal to about 0.1 mm) with an energy source wherein the substrate is manipulated in three dimensions translationally (i.e., along an x-, y-, and/or z-axis) and/or rotationally about an x-, y-, and z-axis according to a manipulation movement algorithm such that a complex shape is defined by means of the energy source interacting with the substrate material, wherein the manipulation movement algorithm is determined using a stochastic optimization framework. In an embodiment, the instant invention may create a three dimensional object which can be used as is or as a mold in a substrate using an electromagnetic radiation source, particle beam radiation, a fluid beam, an ionic beam, abrasion, and/or the like in combination with stochastic optimization computations. In particular, the present invention relates to a method of producing molds for micro machines on the order of 0.1 to 10 mm in one or more dimensions using LiGA (Lithographic (lithography), Galvanoformung (electroplating), Abformung (mold-forming)) in combination with a stochastic optimization framework.
The instant disclosure is relative to the micro scale between 0.1 and about 10 mm, up to a very large scale on the order of meters or more, and may be used on biological systems, as well as to produce micro-machine components.
Micro-Electro-Mechanical Systems (MEMS), also referred to herein as micromachines and/or micromachine systems, comprise a plurality of micro-fabricated components. Micro-fabrication technologies fall into 3 main categories: surface micromachining, bulk micromachining, and micromolding.
Surface micromachining technologies include the patterning of thin films that are deposited on substrates, typically silicon. The devices that are fabricated in this manner are made up of elements that have arbitrary shapes along the plane of the substrate, but have straight sidewalls and are typically on the order of 1 micron thick. The most successful devices fabricated in this manner are made up of 2 or 3 layers and have 1 to about 5 moving parts. This method has not been shown to be able to produce a wide range of devices or systems. The finished devices are part of a substrate and are normally not separated from the substrate, which limits the complexity attainable for micromachine systems fabricated in this manner.
Bulk micromachining techniques entail the patterning of substrates, again mostly silicon, by removing material with a variety of etching methods, e.g. ‘wet’ etching using potassium hydroxide (KOH), tetramethyl ammonium hydroxide (TMAH), ethylenediamine pyrocatechol (EDP), and the like, and/or ‘dry’ etching using reactive ion etch (RIE) plasmas or gases such as XeF2. These methods produce a range of devices including those that work by means of membranes that deform, cantilevered beams that bend, and recently have been used on SOI wafers to create parts that resemble one-layer surface micromachined devices, but which are much thicker and so function better when the driving force is electrostatic attraction, such as stepper motors. The finished devices also usually remain attached to the substrate and are not normally separated from it, again limiting the complexity and range of systems able to be fabricated with these methods.
Micromolding technologies entail methods of creating patterned voids in various materials that are used as ‘molds’ that are subsequently used to fabricate a micromachine part either by electroplating (e.g., LiGA, Su-8 and the like) or by various injection molding techniques. These technologies are capable of creating parts an order of magnitude or more larger than either surface or bulk technologies, and are independent of substrates allowing the parts to be assembled into arbitrarily complex, truly 3-dimensional structures. These techniques are not capable, however, of creating miniature parts of arbitrary geometries, because the “z” or ‘thickness’ dimension, which is the dimension perpendicular to the plane of the substrate, has always been a straight sidewall as a necessary artifact of the technology. Thus, such micromachine parts such as gears can be produced using micromolding, but not spheres, or other parts having a non-linear z-axis or having reentrant angles (e.g., an hour-glass shape) from a single photoresist.
U.S. Pat. Nos. 5,378,583 and 5,496,668 are generally directed to the formation of microstructures, a preformed sheet of photoresist, such as polymethylmethacrylate (PMMA), which is strain free, may be milled down before or after adherence to a substrate to a desired thickness. The photoresist is patterned by exposure through a mask to radiation, such as X-rays, and developed using a developer to remove the photoresist material which has been rendered susceptible to the developer. Micrometal structures may be formed by electroplating metal into the areas from which the photoresist has been removed. The photoresist itself may form useful microstructures, and can be removed from the substrate by utilizing a release layer between the substrate and the preformed sheet which can be removed by a remover which does not affect the photoresist. Multiple layers of patterned photoresist can be built up to allow complex three dimensional microstructures to be formed.
Likewise, U.S. Pat. No. 5,908,719 is generally directed to a procedure for achieving accurate alignment between an X-ray mask and a device substrate for the fabrication of multi-layer microstructures. A first photoresist layer on the substrate is patterned by a first X-ray mask to include first alignment holes along with a first layer microstructure pattern. Mask photoresist layers are attached to second and subsequent masks that are used to pattern additional photoresist layers attached to the microstructure device substrate. The mask photoresist layers are patterned to include mask alignment holes that correspond in geometry to the first alignment holes in the first photoresist layer on the device substrate. Alignment between a second mask and the first photoresist layer is achieved by assembly of the second mask onto the first photoresist layer using alignment posts placed in the first alignment holes in the first photoresist layer that penetrate into the mask alignment holes in the mask photoresist layers. The alignment procedure is particularly applicable to the fabrication of multi-layer metal microstructures using deep X-ray lithography and electroplating. The alignment procedure may be extended to multiple photoresist layers and larger device heights using spacer photoresist sheets between subsequent masks and the first photoresist layer that are joined together using alignment posts.
Accordingly, the method by which complex three-dimensional components may be fabricated involves building up various layers of a mold to produce the desired structure. However, this approach is not only time consuming, but also requires each of the sidewalls to be linear along the z-axis, thus the shape of the wall along the z-axis will be a stepped approximation having a resolution equal to the thickness of the layers, and will not be a true continuous curve.
None of the technologies known in the art are capable of fabricating micromachine parts of arbitrary shape in all dimensions from a single photoresist. As such, the vision of creating true micromachines with many moving parts and a high level of complexity has not been realized. Accordingly, there exists a need for a method of producing micromachine molds and by extension micromachine parts having a continuous non-linear z-axis, preferably from a single layer of a photoresist.